1. Field of the Invention
The present invention relates to a method for detecting a shield in predicting the radio wave propagation characteristics, a system for use with the method, and a recording medium recording an operation control program of the detecting method, and in particular to a method for detecting a shield in predicting the radio wave propagation characteristics by a technique of the geometrical optics.
2. Description of the Prior Art
A radio wave propagation simulator is employed to assist the arrangement of a base station or a host system in a radio communications system. The received power or delay spreading at any receiving point is assessed by using the radio wave propagation simulator to determine an installation site of a due transmitting station, so that the overall efficiency can be enhanced by reducing the number of base stations to be arranged.
The radio wave propagation simulation is largely divided into a statistical technique and a deterministic technique. The former statistical technique gives an expression for estimating the propagation loss with the arguments of distance and frequency to determine the parameters on the basis of a large amount of data resulted from actual measurements of the propagation loss in accordance with the multivariate analysis.
On the other hand, the latter deterministic technique is one in which, considering that the radio wave radiated from an antenna is a collection of a number of radio wave rays, each ray is reflected and transmitted repeatedly on the geometrical optics, and propagated, and the rays incoming to an observation point is synthesized to obtain the propagation loss and the amount of delay. This technique of geometrical optics is further subdivided into an imaging technique and a ray launching technique.
The imaging technique determines a reflection and transmission path of the ray connecting between the transmitting and receiving points by obtaining an imaging point against the reflection surface. Since the reflection and transmission path is uniquely determined if the transmitting and receiving points and the reflecting and transmitting objects are defined, the imaging technique is one of searching for a strict propagation route of the ray. On the other hand, the ray launching technique is one of radiating the ray from an antenna in plural predetermined directions in a manner of time division, irrespective of the receiving point to obtain the propagation route of the ray with the reflection and transmission, and regarding the ray passing near the receiving point as incoming to the receiving point. This was described in particular in the paragraphs “004” to “006” in Japanese Patent Laid-Open No. 9-33584, for example.
The ray launching technique solves approximately, but not strictly like the imaging technique, the propagation route of the ray connecting between the transmitting and receiving points, and has a feature of shortening the time needed to search for the propagation route.
FIG. 8 is a view for explaining the operation of the ray launching technique in the case where an observation area 020, a transmitting point 009, a receiving point 010, and two contents 001, 002 within the observation area are provided. In FIG. 8, for the simplicity, the operation is explained only in the two dimensional plane, but it is common that the operation is performed in the three dimensional space.
First of all, a ray is radiated from the transmitting point 009 in a direction toward the propagation route 003. It is determined from all the contents within the observation area whether or not the ray radiated in that direction strikes the contents existing within the observation area. The ray strikes a content 001 at a reflection point 012, resulting in a transmitted ray 011 and a reflected ray 004. The ray 004 produced by reflection further strikes a content 002, resulting in a transmitted ray 013 and a reflected ray 008 in a similar manner. The reflected ray 008, which passes near the receiving point (observation point) 010, is regarded as the incoming wave in the observation point.
Specifically, the received electric-field strength as defined from a total of propagation distances and a total of incoming delay times of the propagation routes 003, 004 and 008, are recorded in FIG. 9. In FIG. 9, the transverse axis 101 represents the delay time required for the ray to arrive from the transmitting point 009 via the routes 003, 004 and 008 to the observation point 010, and the longitudinal axis 102 represents the received electric-field strength of the ray passing near the observation point 010 and the ray incoming to the observation point 010.
The ray from the transmitting point 009 in the direction toward the propagation route 003 has the transmitted rays 011 and 013, for which the transmission and reflection are repeatedly searched, as in the propagation routes 003, 004 and 008, wherein the ray passing near the receiving point 010 is treated as the incoming wave, as in the propagation route 008, and the above processing is continued till the search end condition is met.
The search end condition is that the received electric-field strength at the reflection and transmission point falls below a predetermined value. After the ray radiated from the transmitting point 009 in the direction toward the propagation route 003 is searched for the routes of the reflection and transmission, the radiation angle of the ray radiated from the transmitting point 009 is changed, as shown in a route 006, for example, and the reflection and transmission routes are similarly searched, investigating all the radiation directions from the transmitting point 009, or partial radiation directions as defined beforehand.
Lastly, FIG. 10 shows a delay profile for the receiving point (observation point) 010. In FIG. 10, the transverse axis 201 represents the delay time when the ray comes in from the transmitting point 009, and the longitudinal axis 202 represents the received electric-field strength of the ray passing near the receiving point 010 and the ray incoming to the receiving point 010. The received power at the receiving point 010 is given by a total of received electric-field strength for all the paths as indicated in FIG. 10, and the delay spreading indicating the distortion is given by the standard deviation of the delay time.
The ray launching technique have to check for all the contents existing within the observation space whether or not the ray strikes the contents to detect the reflecting or transmitting point on the propagation route of the ray. It is necessary to solve multiple variable equations to check whether or not the ray intersects the content within the three dimensional space, which requires a quite amount of computation. That is, to detect the reflected or transmitted point, an expression as defined in the three dimensional space representing the reflection face and an expression as defined in the three dimensional space representing the ray are simultaneously solved as a general calculation technique, bringing about a considerable amount of computation. Hence, there is the problem that the amount of computation needed for the investigation increases with more contents within the observation space, and it takes a lot of time to assess the propagation characteristics.